Field of the Invention
The invention relates to a device for measuring the filling level of a liquid in a container with an ultrasound sensor and electronic components attached to the ultrasound sensor, wherein a damping cup is arranged above the ultrasound sensor.
Brief Discussion of the Related Art
A device of this kind has been described for example in the DE 10 2014 009 610 A1. Such devices are used in particular for measuring the filling level of engine oil in an oil-lubricated engine, in particular in a motor vehicle. The filling level of the liquid is ascertained with the aid of ultrasound sensors. These emit sound waves, which are reflected at the interface between two media, here between air and oil, and which are received back by the ultrasound sensor. The recorded travel time of the sound waves is then used as a basis for ascertaining the filling level in the container holding the liquid. With a running engine, in particular in a motor vehicle, it is difficult, however, to ascertain the filling level of the oil, because the oil is very foamy and the sound waves are reflected at the gas bubbles in the oil. The values detected therefore vary widely across a wide area. In order to obtain measurements which can be evaluated, a unique interface is required between the gaseous medium such as air in this case, and the oil. In order to achieve this, the ultrasound sensors have so-called damping cups assigned to them. The damping cups usually comprise an ante-chamber. Within these damping cups, which surround the measuring section of the ultrasound sensor, the liquid to be measured is calmed and its connection to the container is limited to merely a small opening in the damping cup to the container. Due to the small opening in the damping cup to the container the amount of gas bubbles reaching the damping cup is reduced. The damping cups also serve to retard fluctuations generated e.g. by acceleration or by driving through bends and to take the mean of resulting fluctuations. In order to ensure maximum service life for the device, the ultrasound sensor with its electronic components is overmoulded in one known embodiment using a thermosetting plastic. In order to ensure that subsequent assembly processes can be carried out, the electrical connections are excluded from the overmoulding process.